题解 | #二分查找-II#

import java.util.*;

/**
 * NC105 二分查找-II
 * @author d3y1
 */
public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 如果目标值存在返回下标，否则返回 -1
     * @param nums int整型一维数组 
     * @param target int整型 
     * @return int整型
     */
    public int search (int[] nums, int target) {
        return solution1(nums, target);
        // return solution2(nums, target);
        // return solution3(nums, target);
    }

    /**
     * 二分
     * @param nums
     * @param target
     * @return
     */
    private int solution1(int[] nums, int target){
        int result = -1;

        int n = nums.length;
        if(n == 0){
            return result;
        }
        
        int left = 0;
        int right = n-1;
        int mid;
        while(left <= right){
            mid = (left+right)/2;
            if(nums[mid] < target){
                left = mid + 1;
            }else if(nums[mid] > target){
                right = mid -1;
            }else{
                result = mid;
                right = mid - 1;
            }
        }

        return result;
    }

    /**
     * 二分
     * @param nums
     * @param target
     * @return
     */
    private int solution2(int[] nums, int target){
        int result = -1;

        int n = nums.length;
        if(n == 0){
            return result;
        }

        int left = 0;
        int right = n-1;
        int mid;
        while(left <= right){
            mid = (left+right)/2;
            if(nums[mid] < target){
                left = mid + 1;
            }else{
                right = mid - 1;
            }
        }

        return nums[left]==target ? left : -1;
    }

    /**
     * 二分
     * @param nums
     * @param target
     * @return
     */
    private int solution3(int[] nums, int target){
        int result = -1;

        int n = nums.length;
        if(n == 0){
            return result;
        }

        int left = 0;
        int right = n-1;
        int mid;
        while(left < right){
            mid = (left+right)/2;
            if(nums[mid] < target){
                left = mid + 1;
            }else{
                right = mid;
            }
        }

        return nums[left]==target ? left : -1;
    }
}