LeetCode第34题

常规二分

class Solution {
    public int[] searchRange(int[] nums, int target) {
        if(nums == null || nums.length < 1){
            return new int[]{-1,-1};
        }
        int[] res = new int[]{-1,-1};
        int len = nums.length;
        int left = 0;
        int right = len - 1;
        int mid = (left + right) >> 1;//寻找最小index时，不需要-1，因为右移会向下取整
        while(left < right){//找leftIndex
            if(nums[mid] < target){
                left = mid + 1;
            }
            else if(nums[mid] > target){
                right = mid - 1;
            }else{
                right = mid;
            }
            mid = (left + right) >> 1;
        }
        if(nums[left] == target){
            res[0] = left;
        }
        right = len - 1;
        mid = ((left + right) >> 1) + 1;//因为要寻找最大的index，而右移会向下取整，所以需要+1，不进行+1，会出现死循环的情况
        while(left < right){//找rightIndex
            if(nums[mid] < target){
                left = mid + 1;
            }
            else if(nums[mid] > target){
                right = mid - 1;
            }else{
                left = mid;
            }
            mid = ((left + right) >> 1) + 1;//一定要+1，这是易错点
        }
        if(nums[right] == target){
            res[1] = right;
        }
        return res;
    }
}