④十套《数据结构》练习试题与答案.pdf

1?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.?2?20?1.?()?A.?B.?C.?A.?B.?C.?D.?4.?Amn?A00?644(10)?A22?676(10)?A33(10)?(10)?10?A?688B?678C?692D?6965.?()?A.?B.?C.?D.?7.?18?A19?A1?A?3?()A.1?2?3B.9?5?2?3C.9?5?3D.9?4?2?3?10.?6?()?A.5B.6C.7D.8?1?26?1.?_?_?_?_?2.?(n3+n2log2n+14n)/n2?_?3.?A?C?D?E?F?G?H?I?J?_?_?_?4.?9 2 3+-10 2/-?_?3+4X?-2Y/3?C.?D.D?Amn?A A A A A A A A A A A A A00?644?A A A A A A A A A A A A A A A A A A A A A A A A A A A33 333333 3 33333 3333333 33 3 3 3 3 3 3 3 33(10)?B?676767676767 76767676767676767 767676767676767676767 767 7676767676 6 676 67 7 78C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C8C C8C8C8C C C8C8C8C C8C8C8C8C8C C?692?()()()(?BC.?1 1 1 1 1 1 1 1 1 1 1 1 1 1 18?A A A A A A A A A A A A A A A A A A?3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3?1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1?2 2 2 2 2?35?3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3?2?_?5.?n?_?_?_?6.?n?e?_?_?7.AOV?_?8.?n?_?n?_?9.?(12,23,74,55,63,40)?Key%4?_?_?_?_?10.?B_?_?11.?_?_?12.?_?6?24?1.?A?A0.next?V?E?4.?4,2,5,8,3?7?14?1.LinkList mynote(LinkList L)/L?if(L&L-next)q=L?L=L?next?p=L?S1?while(p?next)p=p?next?S2?p?next=q?q?next=NULL?returnL?1?S1?2?S2?3?a1,a2,?,an?,?_ _ _ _ _ _ _ _ _ _ _ _ _ _?A0.next t t t t t t t t t t t t t t t?V V V V V V V V V V V V V V V V V V V?E?4,4,4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4,4,4 4,4,4,4,4,4,4,4,4,4,4 4,4,4,4,2,2,2 2 2 2,2 2 2 2 2 2 2 2 2 2 2 2 2?7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7?1te(LinkL?3?2.void ABC(BTNode*BT)ifBT ABC(BT-left);ABC(BT-right);coutdata;?8?8?HL?X?X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X?4?1?4?ABCD?CABD?typedef struct int s100;int top;sqstack;void push(sqstack&stack,int x)if(stack.top=m-1)printf(“overflow”);else _;_;?CABD?5?8?1?DFS?BFS?(A?B)?(A?C)?(A?D)?(B?E)?(C?F)?(C?G)?(A?B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B)B B?(A?C)C C)C)C)C)C)C)C)C)C)C)C)C)C)C)C)C C)C C)C)C)C)C)C)C)C)C)C)C C?(A(A(A(A(A(A(A A(A(A(A(A(A A(A(A(A(A(A(A A(A A A(A A(A(A A A(A(A(A A A A A A A A A A?D)D)D)D)D)D)D)D)D)D)D)?(B(B(B(B(B(B(B B(B(B(B(B(B(B(B(B(B(B B(B(B(B B B(B B B B(B(B B B B(B(B(B(B(B(B B(B B(?E)?(C?6?A=(D?R)?D=01?02?03?04?05?06?07?08?09?R=r?r=?2?for?i=1?s=0?i=n?i+?t=1?for(j=1?j=i?j+)t=t*j?s=s+t?n?3?p?A?A?n?e?n?n?e?n?500?n n n n n n n n n n n n n n?e e?n n n n n n n n n n n n n n?n n?7?d?d?_?n?11.?_?=?_?struct recordint key;int others;int hashsqsearch(struct record hashtable,int k)int i,j;j=i=k%p;while(hashtablej.key!=k&hashtablej.flag!=0)j=(_)%m;if(i=j)return(-1);if(_)return(j);else return(-1);?typedef struct nodeint key;struct node*lchild;struct node*rchild;bitree;bitree*bstsearch(bitree*t,intk)if(t=0)return(0);elsewhile(t!=0)if(t-key=k)_;else if(t-keyk)t=t-lchild;else_;?1.?AEFBGCDHIKJ?EFAGBCHKIJD?2?36?15?40?63?22?0.6?H?K?=K mod 7?1?0123456?2?3?10?18?4?3?6?12?1?9?18?8?1?4?444444444444 44 444444444444 4 4 222222222222222222222 2 2 2 2 2?k k k k kek k k k k kekek k k k k k k k k k k y y=y=y=y=k=k=k=k=k=k k=k=k=k=k=k=k k k k k)_)_)_)_)_)_)_)_)_)_)_)_)_)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _;else ie ie i?8?98?9?(20?18?22?16?30?19)?20?_?10?(20?18?22?16?30?19)?_?11?G?n?A?i?j?_?12?A?A?i?0?_?i?0?13?ABCD?BADC?_?14?H(k)=k mod p?hashtalbe?k?0?typedef struct node int key;struct node*next;lklist;void createlkhash(lklist*hashtable)int i,k;lklist*s;for(i=0;im;i+)_;for(i=0;ikey=ai;k=ai%p;s-next=hashtablek;_;?2?(1)?a?(2)?3?ABCDEFGHIJK(a)(b)?k?lklist;_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _;_;_;_;_;_;_;_;_;_;_;_;_;oc(sizeof(l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l(l l l l lkl kl kl kl kl kl kl kl kl kl kl kl kl kl k k kl kl kl kl kl k kl kl kl kl kl k k kl kl kl kl kl kl kl kl k k kl k k k kl kl k k kl l k kl l kl k k k kl kl k k k k k k kl k k k k kl kl kl kl k kl k k klis i is is is is is is is is is is i i is is is i is is is is is is is is is is s s s is s is is s is is s is s s st)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t)t t)t)t)t)t t t t t t t t);););););););););););););););););););););s-s s-s s-s-s s s-s s s s s s-s s s s s s s s s s s key=ai;s-next=hasasasasasasasasasasas sasasasasasasa asasa asa asasasas sas sht ht ht ht ht ht ht ht ht ht ht ht ht ht ht ht t ht ht ht t ht ht ht t ht ht ht ht h ht ht ht ht ht ht t t ht t h h h h h h h h h h ht tababababababab babab bababababababababababab bab bab babababa aba abab b b b b b bab bab b bab b b b b b b b b b b b b ba a le le le e le le le e le le le e le le le e le le e e le le le le le le e e e le le le e le le e le e le le e l le e e e e e e e e ekkkkkkkk kkkkk kkkkk k kkkk kkkk kkkkk k k kkk kk kkkkk k k kk k kk kk k ;_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _?a?10?11?3?(25?50?15?35?80?85?20?40?36?70)?5?2?(A)15?25?35?50?20?40?80?85?36?70(B)15?25?35?50?80?20?85?40?70?36(C)15?25?35?50?80?85?20?36?40?70(D)15?25?35?50?80?20?36?40?70?85?G?E=(a?b)?(a?e)?(a?c)?(b?e)?(e?d)?(d?f)?(f?c)?0?85?G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G?E=E=E=E=E=E=E=E=E=E=E=E=E=E E E E E E=E=E=E E E=E=(a a a a a a a a a a a a a a a?b)b b b b b b)b b b b b)b b b)b)b b)b)b)b)b)b b b)b)b)b)b)b)b)b)b)b)b b b)b b)b b)b)b b)b)b)b)b)b)b)?(a(a(a(?12?void bubble(intrn)for(i=1;i=n-1;i+)for(exchange=0,j=0;jrj+1)temp=rj+1;_;rj=temp;exchange=1;if(exchange=0)return?struct recordint key;int others;int bisearch(struct record r,int k)int low=0,mid,high=n-1;while(low=high)_;if(rmid.key=k)return(mid+1);else if(_)high=mid-1;else low=mid+1;return(0);?G?_ _ _ _ _ _ _;j;j;j j;j;j;j j;j j j;j;j;j j;j;j;j;j;j;j;j;j;j;j;j;j;j j;j;j j j j j;j;j j j+)p=rj+1;_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _;rj j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j=te te te te te te te te te te te e te te te te te te te te te te te te te te te te e te e te te tempm mpmpm mpmpmpm mpmpmpm m m m m m m m m mpmpm m m m m m m m;exchahahaeturn?di i i i i i i i i i i i i nt nt nt nt nt nt nt nt nt nt nt nt nt nt n nt nt nt nt n nt n nt nt t t nt t t t t t k k kek k kek k k kek kekek kek k kek kekek k k k k k k k k k k k k k k k k k k k k k k y;in in in in in n in n in n n n n in in n n n in n n n n n n in n n n n n n n n n n nt ot t t t t t ot t t t t t t t t t t t t t t t t t t t t t t t t t t th th th th th th th th th th h th th h h th th th h h h her er er er er er er er er er er er er er er r er e e s;s;s s;s;s;s;s s s;s;s s s;rch(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(h(s stru u uct c c c c c c ct c c c c ct c c ct ct ct ct t ct t ct ct ct t t t ct t t ct ct t ct ct ct ct t r r r re re re re re re e r r re re re r r re re re e re rec c c coc cocococo ocococ coco d drdrd drdrdrdrd d drdrdrdrdrdrdrdrd d d r r r r r r r r r r r r r r r r r r r,int kt k k kt kt kt k k kt k kt k k kt k k k k k k k)int low w w w w w w w w w w w w w w w w w w w w w w w=0,m,m m m m m m m m m m m m m m m m m m m m m m m,id d d d d d d d d d d d,h,h,h,h,h h,h,h h h h,h,h,h h h h hig ig ig ig ig ig ig g i ig ig i ig i ig g ig g g g i igh=h=h=h=h=h=h=h=h=h=h=h=h=h=h=h n n n n-n-n-n-n-n-n-n-n-n n n-n-n n n-1;1;1;1 1;1 1;1;1;1;1 1;1;1 1 1 1;hile(lo lo lo lo lo lo lo o o o o o o l lo o o o o lo lo o o lo lo lo o o o lo o o o o o lo o lo o lo oww wwwww w ww w ww w w w ww w w w w w ww=h=h=h=ig igh)h)h)_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ey=k=k=k=k=k=k=k=k=k=k=k=k=k=k k k k=k=k k k)r)r)r)r r)r)r)r r)r)r)r)r)r)r r)r)r)r ret et et et e et et et et et et et et et et et et e e et t e u urn13?14?3?head?15?G=?D?R?D=1?2?3?4?5?R=r?r=?_?D=1?2?3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3?4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4?55?R=rr rrrrrrrr rr rrrrrrrrrr rrrrrrrrrrr rr rr r?r?_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _?16?s=i=0?do i=i+1?s=s+i?while(i=n)?le(i=n)?17?struct record int key;datatype others;void quickpass(struct record r,int s,int t,int&i)int j=t;struct record x=rs;i=s;while(ij)while(ix.key)j=j-1;if(ij)ri=rj;i=i+1;while(_)i=i+1;if(ix.kekekeke ekekekekekekekekekekeke ekekekekekek kekekekekekekekeke ek ke eke e ekekey)y)y)y)y)y)y)y)y)y)y)y y)y)y)y y y y)y y)y)y)y)y)y)y)y)y)y)y)y)y)y)y y)j=j=j=j=j=j=j=j=j=j=j=j=j=j j=j=j=j=j=j=j=j=j=j=j=j=j=j j-j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j j 1;if f if if f f if if if if if f f f f f f f if if f if(i(i(i(i(i(i(i i(i(i(i(i(i(i(i(i(i(i i(i(i(i(i i(i(i(i(i(i(i(i(i(i(i i(jjjjjjj jj jjjj jjjjjjjjjjjjj j j jjj jj j)ri=r r rj j j_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _)i=i i i i i i i i i i i i i i+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1 1+1+1+1+1+1 1+1+1+1+1+1+1 1+1 1+1 1;i;f(idata=k;t-lchild=t-rchild=0;else if(t-datak)bstinsert(t-lchild,k);else_;?20?for(i=0?im?i+)for(j=0?jt?j+)cij=0?for(i=0?im?i+)for(j=0?jt?j+)for(k=0?kright=s?s-left=p?p-right-left=s?s-right=p-right?s-left=p?s-right=p-right?p-right=s?p-right-left=s?p-right=s?p-right-left=s?s-left=p?s-right=p-right?s-left=p?s-right=p-right?p-right-left=s?p-right=s?8?m?H(key)=key%p?p?=?eft=s?s-rig ig ig ig ig ig ig ig ig ig ig ig g ig ig g g ig ig ig i ig ig ig ig ig i ig ig ig i ig ig ig ig ig g g g ght ht ht t ht t ht ht ht ht ht ht ht ht t ht ht ht ht ht ht ht ht ht t ht t ht ht t t ht ht t t t t=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p p=p=p=p=p-ri ri ri r ri ri ri ri ri ri r ri ri ri ri ri i ri ri ri r ri ri ri ri r ri ri r ri i i i i ri i i ri i ighghghghghghghghghg ghg ghghghg ghghghghgh hghghghghghgh hg g ghg ghg g g ghg g g g g t?right=s=s=s=s=s s=s s=s=s=s=s=s=s=s=s=s=s s=s=s=?p-right ht ht ht ht h ht ht ht t t ht t ht ht ht ht t t ht ht ht t t ht t t t t t t t t t t ht t-left=s s s s s s s s s s s s?s-lef ef ef ef ef f ef ef ef ef ef ef ef f ef f ef f ef f ef f f ef ef ef ef ef ef f ef f ef f f f f ef f f ft=t=t=t=t=t=t=t=t=t=t=t=t=t t=t=t=t=t=t=t=t=t=t=t=t=t=t=t=t=t=t=t=t p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p?s-right=p p p p p p p p p p p p p p p p p p p p p p p p p p p-ri ri ri ri i ri ri ri i ri ri ri ri ri ri ri ri ri i ri ri ri ri ri ri ri r ri i ri ri i i i ri r r ri r ghghghghghghghghghghghghghghghghghg ghg ghghghghghghghghghghghghgh hgh h hgh h h hg gh hghght t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t t?ht?p-right ht ht ht ht ht h h ht ht h ht ht h ht ht ht ht h ht ht t t t h ht t t t t t t t t-le le le le le le le le le le l le le le le le le le le l le e le le le le le le le le le le l l le le le le le e e l l left f f ft ft ft ft f ft f f f f ft f f f ft ft f ft ft f f ft f ft f ft ft ft ft ft ft f ft ft f ft=s=s=s=s=s=s=s=s=s=s s=s=s=s=s=s s=s=s s s s s s s s s s s?p-r rig ig g ig ig ig ig ig ig g ig ig g ig g ig ig ig ig ig ig g ig ig ig ig ig ig ig g i ig g i ht ht h ht ht ht ht ht ht ht ht ht ht ht ht ht ht ht ht h ht ht ht ht ht ht ht h ht ht ht h h h ht h ht h ht h h=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=s=?m m m m m?H(H H H H H H H key)=?21?22?23?i=0?s=0?while(sdata=ch;_;createbitree(bt-rchild);14.?typedef struct node int data;struct node*next;lklist;void lklistcreate(_*&head)for(i=1;idata);p-next=0;if(i=1)head=q=p;else q-next=p;_;?pedef st s st st st st st st st st st st st st st st st st t st st st st truct ct ct ct t t t ct ct t t ct t t t ct t t t ct t t t ct t n no onon dedededededededededededededed de e e e ei i i i i i i i i i i i i i int nt nt nt nt t nt nt nt nt nt nt t nt t nt n n dadad d dadadadadada adadadadad dadadadata ta a ta ta t ta ta ta t ta t t t;s s;tr r r r r r r r r r r r ru u ucu u u u u u u ucu u u u u u u u u u u u t n n n n n n n n n n n n n n no o o odo o o o o o o o o o o o o e*lc l lccrea a a a a a a a a a a a a a a a at t t te e e e te e e t t te e e e e e e te t te te e e e e e e e e e t t t t t t t bi bi b bi bi bi b bi bi bi bi bi b b bi b bi bi bi b bi b bi b b bi bi b bi b b b tr tr tr tr tr tr tr tr tr tr tr tr tr r tr tr tr tr tr r reeeeeee e e e e e e e e e e(b(b bit t itre re re re re re e re re re re re e re re r re ee e*e*e*e*e*e*e*e*e*e*e*e*e*e*e e*e*e*e e*&b&b&b&b&b&b&b&b&b&b&b&b&b&b b&b bt)t)t)t)t)t)t)t)t)%c”c”c”c”c”c”c”c”c”c”c”c”c”c c c c c,&,&,&,&,&,&,&,&,&,ch h h);)_;alloc(s25?2?26?2?20?1.A2.D3.D4.C5.C6.D7.D8.C9.D10.A?1?26?6?24?1.?78?50?40?60?34?90?#%&0111010101110111010101110?113.?(1,2)3,(4,6)4,(1,3)5,(1,4)8,(2,5)10,(4,7)204.?12?124444422255522884352834?90?#010 01010101010 0101010101010101010 0101010101010 01010 010 0 0 0 0101010 0 01011101 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11111?27?7?14?1.?1?2?3?a2,a3,?,an,a1?2.?2?8?8?int CountX(LNode*HL,ElemType x)int i=0;LNode*p=HL;/i?while(p!=NULL)if(P-data=x)i+;p=p-next;/while,?i?x?return i;/CountX?2.q-llink=p;q-rlink=p-rlink;p-rlink-llink=q;p-rlink=q;?5.E=(1?3)?(1?2)?(3?5)?(5?6)?(6?4)6.?28void quickpass(int r,int s,int t)int i=s,j=t,x=rs;while(ij)while(ix)j=j-1;if(ij)ri=rj;i=i+1;while(ij&rix)i=i+1;if(inext)for(q=hb;q!=0;q=q-next)if(q-data=p-data)break;if(q!=0)t=(lklist*)malloc(sizeof(lklist);t-data=p-data;t-next=hc;hc=t;?=p-da a a a a a a a a a a a a a ada a a a a a a a a a a a a a a a a a a a a ata ta ta ta ta ta ta ta ta ta ta a ta a ta ta ta ta ta a ta ta ta ta a a ta ta a ta ta t ta t)b b)b)b)b)b)b)b b b b b b)b b b b)b b b b)b b b)b b b b b b)b b)b b b b)b b b)reak;f(lklist);t-da a a a a a a a a a a a a a a a a a a a a a a a ata ta ta ta ta ta ta ta ta ta ta ta ta ta t ta ta ta ta t ta t t ta t ta ta t t ta ta t t t t=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p=p p=p p p=p p p p-dadadadadadadadadadada ada adadadadadadadadadadadada adadadadadada a a a a a a ata ta ta ta ta ta ta ta ta ta ta ta a a ta ta ta a a ta ta ta ta ta ta a ta a ta ta ta a ta a a a t t t t t t;t-nenenenenenenenenenenenenenenen nenenen nenenen nene e enene e ene ext xt x xt xt xt xt xt xt xt xt xt xt xt xt xt t xt xt t t xt xt t xt t xt xt xt t xt xt xt xt xt t t t t xt t=h=h=h=h=h=h=h=h=h=h=h=h=h=h=h=h=h=h h=h=c;hc=t=t=t;?29?j+1?hashtablej.key=k?1?2?H(36)=36 mod 7=1;H?(22)=(1+1)mod 7=2;.?H(15)=15 mod 7=1;.?H2(22)=(2+1)mod 7=3;H?(15)=(1+1)mod 7=2;H(40)=40 mod 7=5;H(63)=63 mod 7=0;H(22)=22 mod 7=1;.?1?01234566336152240?2?ASL=6.1531121?!3?(8,9,4,3,6,1),10,(12,18,18)(1,6,4,3),8,(9),10,12,(18,18)1,(3,4,6),8,9,10,12,18,(18)1,3,(4,6),8,9,10,12,18,181,3,4,6,8,9,10,12,18,18?typedef int datatype;typedef struct node datatype data;struct node*next;lklist;void delredundant(lklist*&head)?H H H H H H?(22)=(1+1)1)1)1)1)1)1)1)1)1)1)1)1)1)1)1 1)1)1)1)1 1)1)1)1 1)1 1 1 mom m m m m m m m m m m m m m m m m m m m m m m m m d 7=2 2 2;.?H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H2(22)=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(=(2+2+2+2+2+2+2+2 2 2+2+2+2 2+2+2+2 2 2+2 2+2+2+2 2+2 2 2+2 2+2+2+2 2+2+2 2 2 2+2 2 2 2 2 1)mod 7mod 7=2;mo od 7d 7d 7d 7d 7d 7 7d 7d 7d 7d 7d 7d 7 7d 7d 7d 7d 7d 7d 7 7d 7d 7d 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7=5=5=5=5 5 5 5=5=5=;3 mom m m m m m m m m m m m m m m m m m m m m m m m d 7 7 7 7 7 7 7 7 7 7 7 7 7 7