移除元素

移除元素（leetcode27）

var removeElement = function(nums, val) {
    const n = nums.length;
    let left = 0;
    for (let right = 0; right < n; right++) {
        if (nums[right] !== val) {
            nums[left] = nums[right];
            left++;
        }
    }
    return left;
};

删除有序数组中的重复项（leetcode26）

/**
 * @param {number[]} nums
 * @return {number}
 */
var removeDuplicates = function(nums) {
    const n = nums.length;
    if (n === 0) {
        return 0;
    }
    let fast = 1, slow = 1;
    while (fast < n) {
        if (nums[fast] !== nums[fast - 1]) {
            nums[slow] = nums[fast];
            ++slow;
        }
        ++fast;
    }
    return slow;
};

移动0（leetcode283）

/**
 * @param {number[]} nums
 * @return {void} Do not return anything, modify nums in-place instead.
 */
var moveZeroes = function(nums) {
    let slowIndex = 0;
    for (let fastIndex = 0; fastIndex < nums.length; fastIndex++) {
        if (nums[fastIndex] !== 0) {
            [nums[slowIndex], nums[fastIndex]] = [nums[fastIndex], nums[slowIndex]];
            slowIndex++;
        }
    }
};

比较含退格的字符串（leetcode844）

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var backspaceCompare = function(S,T) {
    let i = S.length - 1,
        j = T.length - 1,
        skipS = 0,
        skipT = 0;
    //大循环
    while(i >= 0 || j >= 0) {
        // S 循环
        while(i >= 0) {
            if(S[i] === '#') {
                skipS++;
                i--;
            } else if(skipS > 0) {
                skipS--;
                i--;
            } else break;
        }
        // T 循环
        while(j >= 0) {
            if(T[j] === '#') {
                skipT++;
                j--;
            } else if(skipT > 0) {
                skipT--;
                j--;
            }else break;
        }
        if(S[i] !== T[j]) return false;
        i--;
        j--;
    }
    return true;
};

有序数组的平方（leetcode977）

/**
 * @param {number[]} nums
 * @return {number[]}
 */
var sortedSquares = function(nums) {
    const n = nums.length;
    const ans = Array(n);
    let i = 0, j = n - 1;
    for (let p = n - 1; p >= 0; p--) {
        const x = nums[i] * nums[i];
        const y = nums[j] * nums[j];
        if (x > y) {
            ans[p] = x;
            i++;
        } else {
            ans[p] = y;
            j--;
        }
    }
    return ans;
};