常用库函数的编写

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1、strcpy

2、strcmp

int strcmp(const char* str1,const char* str2){assert(str1!=NULL && str2!=NULL);while(*str1 && *str2 && *str1 == *str2){str1++;str2++;}int res = *str1 - *str2;if(res > 0)return 1;if(res < 0)return -1;return 0;}

、strcat

、strstr

、strlen

int strlen(const char* str){assert(str != NULL);int len = 0;while(*str){len++;str ++;}return len;}

、strncpy

、memset

void* memset(void* src,int c,unsigned int length){assert(src != NULL);char* s = (char*)src;while (length --){*s = (char)c;s = s + 1;}return src;}

、atoi

、itoa

、power

、sqrt

leetcode之sqrt实现

class Solution {public:    int sqrt(int x) {        // IMPORTANT: Please reset any member data you declared, as        // the same Solution instance will be reused for each test case.        long long a = 0,x2=(long long )x,b = x2,mid=0;while(a<=b){mid = (a+b)/2;long long  temp = mid * mid;if(temp == x2 || temp < x2 && (mid+1)*(mid+1)>x2) break;else if(temp<x2)a= mid+1;else b = mid-1;}return (int)mid;    }};

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