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Sub64.java
75 lines (67 loc) · 2.04 KB
/
Sub64.java
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package com.easy.leetcode;
/*
64. 最小路径和
给定一个包含非负整数的 m x n 网格,请找出一条从左上角到右下角的路径,使得路径上的数字总和为最小。
说明:每次只能向下或者向右移动一步。
示例:
输入:
[
[1,3,1],
[1,5,1],
[4,2,1]
]
输出: 7
解释: 因为路径 1→3→1→1→1 的总和最小。
*/
public class Sub64 {
public static void main(String[] args) {
Solution_64_2 solution = new Solution_64_2();
int[][] grid = new int[][]{{1, 3, 1}, {1, 5, 1}, {4, 2, 1}};
System.out.println("返回结果为:" + solution.minPathSum(grid));
}
}
/**
* 动态规划(新建二维数组)
*/
class Solution_64_1 {
public int minPathSum(int[][] grid) {
int n = grid.length, m = grid[0].length;
int[][] dp = new int[n][m];
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (i == 0 && j == 0) {
dp[i][j] = grid[i][j];
} else if (i == 0) {
dp[i][j] = dp[i][j - 1] + grid[i][j];
} else if (j == 0) {
dp[i][j] = dp[i - 1][j] + grid[i][j];
} else {
dp[i][j] = Math.min(dp[i][j - 1], dp[i - 1][j]) + grid[i][j];
}
}
}
return dp[n - 1][m - 1];
}
}
/**
* 动态规划(改进)
*/
class Solution_64_2 {
public int minPathSum(int[][] grid) {
int n = grid.length, m = grid[0].length;
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
if (i == 0 && j == 0) {
continue;
} else if (i == 0) {
grid[i][j] = grid[i][j - 1] + grid[i][j];
} else if (j == 0) {
grid[i][j] = grid[i - 1][j] + grid[i][j];
} else {
grid[i][j] = Math.min(grid[i][j - 1], grid[i - 1][j]) + grid[i][j];
}
}
}
return grid[n - 1][m - 1];
}
}