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triangle.cpp
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triangle.cpp
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// =====================================================================================
//
// Filename: triangle.cpp
//
// Description: 120. 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.
//
// Version: 1.0
// Created: 08/19/2019 05:48:16 PM
// Revision: none
// Compiler: g++
//
// Author: Zhu Xianfeng (), [email protected]
// Organization:
//
// =====================================================================================
#include <stdio.h>
#include <algorithm>
#include <vector>
using std::vector;
class Solution1
{
public:
int minimumTotal(vector<vector<int>>& triangle)
{
if (triangle.size() == 0 || triangle[0].size() == 0)
{
return 0;
}
vector<vector<int>> sums;
sums.push_back(triangle[0]);
for (int i = 1; i < triangle.size(); i++)
{
const auto& row = triangle[i];
sums.push_back(vector<int>(row.size()));
sums[i][0] = sums[i - 1][0] + row.front();
sums[i][row.size() - 1] = sums[i - 1][row.size() - 2] + row.back();
for (int j = 1; j < row.size() - 1; j++)
{
sums[i][j] = std::min(sums[i - 1][j - 1], sums[i - 1][j]) + row[j];
}
}
const auto& last_row = sums.back();
int min_sum = last_row[0];
for (int i = 1; i < last_row.size(); i++)
{
if (last_row[i] < min_sum)
{
min_sum = last_row[i];
}
}
return min_sum;
}
};
class Solution2
{
public:
int minimumTotal(vector<vector<int>>& triangle)
{
if (triangle.size() == 0 || triangle[0].size() == 0)
{
return 0;
}
vector<int> sums(triangle.back());
for (int i = triangle.size() - 2; i >= 0; i--)
{
const auto& row = triangle[i];
for (int j = 0; j < row.size(); j++)
{
sums[j] = std::min(sums[j], sums[j + 1]) + row[j];
}
}
return sums[0];
}
};
using Solution = Solution2;
int main(int argc, char* argv[])
{
vector<vector<int>> triangle = {
{2},
{3, 4},
{6, 5, 7},
{4, 1, 8, 3},
};
int min_sum = Solution().minimumTotal(triangle);
printf("Minimum path sum: %d\n", min_sum);
return 0;
}