【DP】LCR 100.三角形最小路径和

题目

DP

Python

class Solution:
    def minimumTotal(self, triangle: List[List[int]]) -> int:
        n = len(triangle)
        dp = triangle.copy()
        for i in range(1, n):
            for j in range(i+1):
                if j == 0:
                    dp[i][j] = dp[i-1][0] + triangle[i][j]
                elif j == i:
                    dp[i][j] = dp[i-1][j-1] + triangle[i][j]
                else:
                    dp[i][j] = min(dp[i-1][j-1], dp[i-1][j]) + triangle[i][j]
        return min(dp[n-1])

Java

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        int n = triangle.size();
        if (n == 1) {
            return triangle.get(0).get(0);
        }
        int[] tmp = new int[n];
        tmp[0] = triangle.get(0).get(0);
        int ans = Integer.MAX_VALUE;
        for (int i = 1; i < n; ++i) {
            for (int j = i; j >= 0; --j) {
                if (j == i) {
                    tmp[j] = tmp[j - 1] + triangle.get(i).get(j);
                } else if (j < i && j > 0) {
                    tmp[j] = Math.min(tmp[j], tmp[j - 1]) + triangle.get(i).get(j);
                } else if (j == 0) {
                    tmp[j] = tmp[j] + triangle.get(i).get(j);
                }
                if (i == n - 1) {
                    ans = Math.min(ans, tmp[j]);
                }
            }
        }

        return ans;
    }
}