Search for a range

最新推荐文章于 2018-05-15 23:04:11 发布

转载最新推荐文章于 2018-05-15 23:04:11 发布 · 333 阅读

Leetcode 同时被 3 个专栏收录

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Array

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二分Binary Search

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本文详细介绍了二分查找算法的基本原理，并通过实例展示了如何避免边界溢出问题，同时探讨了二分查找在搜索范围内的优化应用。

两次二分

array的题每次写循环的时候都要注意有没有index out of bound的可能！！

public class Solution {
    public int[] searchRange(int[] A, int target) {
        int[] res = new int[2];
        res[0] = -1;
        res[1] = -1;
        
        int beg = 0;
        int end = A.length - 1;
        int s = -1;
        
        while (beg <= end) {
            s = (beg + end)/2;
            if (A[s] > target) {
                end = s - 1;
            } else if (A[s] < target) {
                beg = s + 1;
            } else {
                 //save the result
        int temp = s;
        res[0] = s;
        res[1] = s;
                
        //search towards right
        int rbeg = temp + 1;
        while ( rbeg <= end) {
            s = (rbeg + end)/2;
            if (A[s] == target && (s == end || A[s+1] > target)){
                res[1] = s;
                break;
            }
            if (A[s] == target) {
                rbeg = s + 1;
            } else {
                end = s - 1;
                }
            }
                
        // search towards left
        int lend = temp -1;
        while (beg <= lend){
            s = (beg + lend)/2;
            if (A[s] == target && (s == beg || A[s-1] < target)){
                res[0] = s;
                break;
            }
            if (A[s] == target) {
                lend = s - 1;
            } else {
                beg = s + 1;
                }
            }
            break;
        }
    }
    
     return res;
    }
}