算法训练营第一天|LeetCode704 二分查找、LeetCode27 移除元素、LeetCode977 有序数组的平方

Leetcode74 二分查找

思路

重点在于：

1. Search range 减小
2. Solution不能被排除

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

Leetcode27 移除元素

一开始肯定想到的是暴力解法 学会用双指针思考

class Solution {
    public int removeElement(int[] nums, int val) {
        int slow = 0;
        for(int i = 0; i < nums.length; i++) {
            if(nums[i] != val) {
                nums[slow++] = nums[i];
            }
        }
        return slow;
    }
}

Leecode977 有序数组的平方

双指针的妙用，结果数组从最末端开始遍历

class Solution {
    public int[] sortedSquares(int[] nums) {
        int left = 0;
        int right = nums.length - 1;
        int[] result = new int[nums.length];
        int resultIndex = nums.length - 1;
        while(left <= right) {
            if(nums[left] * nums[left] <= nums[right] * nums[right]) {
                result[resultIndex--] = nums[right] * nums[right];
                right--;
            } else {
                result[resultIndex--] = nums[left] * nums[left];
                left++;
            }
        }
        return result;
    }
}