二分法的最简洁写法

 

一

def lower_bound(array, first, last, value): # 返回[first, last)内第一个不小于value的值的位置
    while first < last: # 搜索区间[first, last)不为空
        mid = first + (last - first) // 2  # 防溢出
        if array[mid] < value: first = mid + 1
        else: last = mid
    return first  # last也行，因为[first, last)为空的时候它们重合

二

public int firstOccurrence(int[] nums, int target) {
    int low = 0, high = nums.length-1;
    while (low <= high) {
        int mid = low + (high - low) / 2;
        if (nums[mid] < target) { low = mid + 1; }
        if (nums[mid] >= target) { high = mid - 1; }
    }
    return low;
}

参考：

 https://www.zhihu.com/question/36132386/answer/530313852