leetcode 35. Search Insert Position搜索插入位置(二分查找)

问题描述：

  Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.

  You may assume no duplicates in the array.

思路一：

从左到右直接搜索

代码一：

class Solution {
    public int searchInsert(int[] nums, int target) {
        if(nums == null) return 0;
        for(int i = 0; i < nums.length; i++){
            if(nums[i] == target)
                return i;
        }
        if(nums[0] > target) return 0;
        if(nums[nums.length-1] < target) return nums.length;
        for(int i = 0; i < nums.length; i++){
            if(nums[i] 1] > target)
                return i+1;
        }
        return 0;
    }
}

代码二：

class Solution {
    public int searchInsert(int[] nums, int target) {
        if(nums == null) return 0;
        int i;
        for(i = 0; i < nums.length; i++){
            if(nums[i] >= target)
                return i;
        }
        return i;
    }
}

思路二：

二分查找

代码三：

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