标签：while   最小   个数   存在   错误   大于   pre   binary   ret   

二分憨批一号！

今天写尼玛的二分竟然wa了好几发

易发生错误：

1，右边界不够。（一开始1e18一直wa,2e18过的）

2，逻辑错误。

/*
几种二分方法整理
元素可以重复 
*/
 
//lower_bound(num, num+size, x)-num:大于等于x的第一个数的下标 
//upper_bound(num, num+size, x)-num:大于x的第一个数的下标 
 
//1.求等于x的最小的index，不存在返回-1
int binary (int *num, int start, int end, int x) {
    int l = start, r = end, ans=-1;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] == x) {
            ans = mid;
            r = mid - 1;
        }
        else if(num[mid] > x)
            r = mid - 1;
        else
            l = mid + 1;
    }
    return ans;
}
 
//2.求等于x的最大的index，不存在返回-1
int binary (int *num, int start, int end, int x) {
    int l = start, r = end, ans=-1;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] == x) {
            ans = mid;
            l = mid + 1;
        }
        else if(num[mid] > x)
            r = mid - 1;
        else
            l = mid + 1;
    }
    return ans;
}
 
//3.求小于x的最大的index
int binary (int *num, int start, int end, int x) {
    int l = start, r = end;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] >= x)
            r = mid - 1;
        else
            l = mid + 1;
    }
    return r;
}
 
//4.求大于x的最小的index
int binary (int *num, int start, int end, int x) {
    int l = start, r = end;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] <= x)
            l = mid + 1;
        else
            r = mid - 1;
    }
    return l;
}
 
//5.求大于等于x的最小的index
int binary (int *num, int start, int end, int x) {
    int l = start, r = end;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] >= x)
            r = mid - 1;
        else
            l = mid + 1;
    }
    return l;
}
 
//6.求小于等于x的最大的index
int binary (int *num, int start, int end, int x) {
    int l = start, r = end;
    while(l <= r) {
        int mid = (l+r) >> 1;
        if(num[mid] <= x)
            l = mid + 1;
        else
            r = mid - 1;
    }
    return r;
}

今日憨批++

二分总结！！

标签：while   最小   个数   存在   错误   大于   pre   binary   ret   

原文地址：https://www.cnblogs.com/flexible-perseverance/p/12302033.html