【代码随想录】day45

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一、70爬楼梯 （进阶）

去年春招面试被考过这个题，但当时没写出来。

#include <vector>
#include <iostream>
using namespace std;
int main() {
    int n, m;
    cin >> n >> m;
    std::vector<int> dp(n + 1, 0);
    dp[0] = 1;
    for (int i = 1; i < n + 1; i ++) {
        for (int j = 1; j < m + 1; j ++) {
            if (i - j >= 0) {
                dp[i] += dp[i-j];
            }
        }
    }
    cout << dp[n] << endl;
}

二、322零钱兑换

class Solution {
public:
    int coinChange(vector<int>& coins, int amount) {
        vector<int> dp(amount + 1, INT_MAX - 1);
        dp[0] = 0;
        for (int j = coins[0]; j < amount + 1; j ++) {
            if (j % coins[0] == 0) {
                dp[j] = j / coins[0];
            }
        }
        for (int i = 1; i < coins.size(); i ++) {
            if (coins[i] > amount) {
                continue;
            }
            for (int j = 1; j < amount + 1; j ++) {
                if (j >= coins[i]) {
                    dp[j] = min(dp[j], 1 + dp[j-coins[i]]);
                }
            }
        }
        if (dp[amount] == INT_MAX - 1) return -1;
        return dp[amount];
    }
};

初始化总是写不好啊。。。

class Solution {
public:
    int coinChange(vector<int>& coins, int amount) {
        vector<int> dp(amount + 1, INT_MAX);
        dp[0] = 0;
        for (int i = 0; i < coins.size(); i ++) {
            if (coins[i] > amount) {
                continue;
            }
            for (int j = coins[i]; j < amount + 1; j ++) {
                if (dp[j-coins[i]] != INT_MAX) {
                    dp[j] = min(dp[j], 1 + dp[j-coins[i]]);
                }
            }
        }
        if (dp[amount] == INT_MAX) return -1;
        return dp[amount];
    }
};

三、279完全平方数

class Solution {
public:
    int numSquares(int n) {
        //<=100
        vector<int> dp(n + 1, 0);
        for (int j = 1; j < n + 1; j ++) {
            dp[j] = j;
        }
        for (int i = 1; i <= 100 && i * i <= n; i ++) {
            for (int j = i*i; j < n + 1; j ++) {
                dp[j] = min(dp[j], 1 + dp[j-i*i]);
            }
        }
        return dp[n];
    }
};

修改初始化：

class Solution {
public:
    int numSquares(int n) {
        vector<int> dp(n + 1, INT_MAX);
        dp[0] = 0;
        for (int i = 1; i <= 100 && i * i <= n; i ++) {
            for (int j = i*i; j < n + 1; j ++) {
                dp[j] = min(dp[j], 1 + dp[j-i*i]);
            }
        }
        return dp[n];
    }
};