[LeetCode][JavaScript]Triangle

Triangle

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.

For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

 

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

Note:
Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

https://leetcode.com/problems/triangle/

 

 

---

 

 

 

动态规划，找个规律。

每一层都基于上一层的最小和来推断当前的最小和。

第一个点的min只能是上层的结果加上自己；最后一个点的min只能是上层的结果加上自己;中间的点就2个选择，上层对应下标的点和(对应下标 - 1)的点。

/**
 * @param {number[][]} triangle
 * @return {number}
 */
var minimumTotal = function(triangle) {
    var passed = triangle[0];
    if(triangle.length === 1){
        return passed[0];
    }
    var min = Infinity;
    for(var i = 1; i < triangle.length; i++){
        var row = triangle[i];
        var currRow = [];
        for(var j = 0; j < row.length; j++){
            var tmp = null;
            if(j === 0){
                tmp = row[0] + passed[0];
            }else if(j === row.length - 1){
                tmp = row[j] + passed[j - 1];
            }else{
                tmp = Math.min(row[j] + passed[j], row[j] + passed[j - 1]);
            }
            currRow.push(tmp);
            if(i === triangle.length - 1){
                if(tmp < min){
                    min = tmp;
                }
            }
        }
        passed = currRow;
    }
    return min;
};