[LeetCode][JavaScript]Candy

Candy 

There are N children standing in a line. Each child is assigned a rating value.

You are giving candies to these children subjected to the following requirements:

• Each child must have at least one candy.
• Children with a higher rating get more candies than their neighbors.

What is the minimum candies you must give?

https://leetcode.com/problems/candy/

 

 

 

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贪心，想通了两轮遍历完事。

第一轮第一个小盆与先给1根，从左往右扫，如果发现当前的rating小于左边的rating，给的糖比左边的多1。

第二轮从倒数第二个小盆与开始，从右往左扫，如果发现当前的rating小于右边的rating，并且糖也少，给的糖比左边的多1。

/**
 * @param {number[]} ratings
 * @return {number}
 */
var candy = function(ratings) {
    var i, result; rates = [];
    rates[0] = 1;
    for(i = 1; i < ratings.length; i++){
        if(ratings[i] > ratings[i - 1]){
            rates[i] = rates[i - 1] + 1;
        }else{
            rates[i] = 1;
        }
    }
    result = rates[ratings.length - 1];
    for(i = ratings.length - 2; i >= 0; i--){
        if(ratings[i] > ratings[i + 1] && rates[i] <= rates[i + 1]){
            rates[i] = rates[i + 1] + 1;
        }
        result += rates[i];
    }
    return result;
};

 

一开始想了一个解法，有点费劲。

第一轮遍历，如果这个小盆与比左右的rating都要小，他肯定是1，把index加入到queue中。

然后就开始递归，有点像bfs。

这样递归的话，保证大的rating一定后做，先处理的是较小的rating。

递归的时候分两种情况：

1. 当前ratings小于左边且大于右边 或者 当前ratings小于右边且大于左边。

因为大的一定后做，所以可以确定当前点的糖数，等于max(左边糖，右边糖) + 1，注意这里如果还没有给过糖，默认值是0，较大的一边是0。

2. 如果两边都给过糖了，并且当前ratings大于左边且大于右边，当前节点的糖数也是等于max(左边糖，右边糖) + 1。

这一轮给完糖后，把左边右边和当前的没有发过糖的节点都塞进queue中。

虽然比较复杂，时间复杂度仍然是O(n)。

但是交上去之后12000的那组数据堆栈溢出。

唉，本地测试10几毫秒妥妥的，leetcode的JS小堆栈居然爆了，是在下输了。

/**
 * @param {number[]} ratings
 * @return {number}
 */
var candyMLE = function(ratings) {
    var queue = [], result = 0, rates = [];
    for(var i = 0; i < ratings.length; i++){
        if(ratings[i - 1] && ratings[i - 1] < ratings[i]){
            continue;
        }
        if(ratings[i + 1] && ratings[i + 1] < ratings[i]){
            continue;
        }
        queue.push(i);
        result++;
        rates[i] = 1;
    }
    bfs(queue);
    return result;

    function bfs(queue){
        var len = queue.length;
        if(queue.length !== 0){
            while(len--){
                var top = queue.shift();
                if(!rates[top]){
                    giveCandy(queue, top);
                }
                if(!rates[top - 1] && ratings[top - 1] && queue.indexOf(top - 1) === -1){
                    queue.push(top - 1);
                }
                if(!rates[top + 1] && ratings[top + 1] && queue.indexOf(top + 1) === -1){
                    queue.push(top + 1);
                }   
                if(!rates[top] && queue.indexOf(top) === -1){
                    queue.push(top);
                }     
            }
            bfs(queue);    
        }
    }
    function giveCandy(queue, i){
        if(ratings[i]){            
            var leftValue = ratings[i - 1] || 0;
            var leftRate = rates[i - 1] || 0;
            var rightValue = ratings[i + 1] || 0;
            var rightRate = rates[i + 1] || 0;
            if(ratings[i] > leftValue && ratings[i] < rightValue || 
                ratings[i] < leftValue && ratings[i] > rightValue ||
                ratings[i] >= leftValue && ratings[i] >= rightValue && (leftRate !== 0 || !ratings[i - 1])){
                rates[i] = Math.max(leftRate, rightRate) + 1;
                result += rates[i];
            }
        }
    }
};