62. 不同路径

class Solution {
    public int uniquePaths(int m, int n) {
        int[][] dep = new int[m][n];
        for (int i = 0;i < m;i++){
            dep[i][0] = 1;
        }
        for (int j = 1;j < n;j++){
            dep[0][j] = 1;
        }
        for (int i = 1;i < m;i++){
            for (int j = 1;j < n;j++){
                dep[i][j] = dep[i - 1][j] + dep[i][j - 1];
            }
        }
        return dep[m-1][n-1];
    }
}

63. 不同路径 II

class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        if (obstacleGrid[0][0] == 1){
            return 0;
        }
        obstacleGrid[0][0] = 1;
        for (int i = 1;i < m;i++){
            obstacleGrid[i][0] = (obstacleGrid[i][0] == 0 && obstacleGrid[i - 1][0] == 1) ? 1 : 0;
        }
        for (int j = 1;j < n;j++){
            obstacleGrid[0][j] = (obstacleGrid[0][j] == 0 && obstacleGrid[0][j - 1] == 1) ? 1 : 0;
        }
        for (int i = 1;i < m;i++){
            for (int j = 1;j < n;j++){
                if (obstacleGrid[i][j] == 0){
                    obstacleGrid[i][j] = obstacleGrid[i - 1][j] + obstacleGrid[i][j - 1];
                }else{
                    obstacleGrid[i][j] = 0;
                }
            }
        }
        return obstacleGrid[m - 1][n - 1];
    }
}

64. 最小路径和

class Solution {
    public int minPathSum(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        int[][] dp = new int[m][n];
        dp[0][0] = grid[0][0];
        for (int i = 1;i < m;i++){
            dp[i][0] = dp[i-1][0] + grid[i][0];
        }
        for (int j = 1;j < n;j++){
            dp[0][j] = dp[0][j-1] + grid[0][j];
        }
        for (int i = 1;i < m;i++){
            for (int j = 1;j < n;j++){
                dp[i][j] = Math.min(dp[i - 1][j],dp[i][j - 1]) + grid[i][j];
            }
        }
        return dp[m-1][n-1];
    }
}

121. 买卖股票的最佳时机

class Solution {
    public int maxProfit(int[] prices) {
        if (prices.length <= 1){
            return 0;
        }
        int res = 0;
        int num = prices[0];
        for (int i = 1;i < prices.length;i++){
            if (prices[i] < num){
                num = prices[i];
            }else {
                res = Math.max(res,prices[i] - num);
            }
        }
        return res;
    }
}

122. 买卖股票的最佳时机 II

class Solution {
    public int maxProfit(int[] prices) {
        if (prices.length <= 1){
            return 0;
        }
        int res = 0;
        for (int i = 1;i < prices.length;i++){
            if (prices[i] > prices[i - 1]){
                res += prices[i] - prices[i - 1];
            }
        }
        return res;
    }
}

53. 最大子序和

class Solution {
    public int maxSubArray(int[] nums) {
        int sum = 0;
        int ans = nums[0];
        for (int num : nums){
            if (sum > 0){
                sum += num;
            }else{
                sum = num;
            }
            ans = Math.max(ans, sum);
        }
        return ans;
    }
}

322. 零钱兑换

class Solution {
    public int coinChange(int[] coins, int amount) {
        if (amount == 0){
            return 0;
        }
        int[] dp = new int[amount + 1];
        for (int coin : coins){
            for (int i = coin;i <= amount;i++){
                if (i == coin){
                    dp[i] = 1;
                }else if (dp[i] == 0 && dp[i - coin] != 0){
                    dp[i] = dp[i -coin] + 1;
                }else if (dp[i - coin] != 0){
                    dp[i] = Math.min (dp[i], dp[i -coin] + 1);
                }
            }
        }
        return dp[amount] == 0 ? -1 : dp[amount]; 
    }
}

518. 零钱兑换 II

class Solution {
    public int change(int amount, int[] coins) {
        int[] dp = new int[amount + 1];
        dp[0] = 1;
        for (int coin : coins){
            for (int i = coin;i <= amount;i++){
                dp[i] += dp[i - coin]; 
            }
        }
        return dp[amount]; 
    }
}

1143. 最长公共子序列

300. 最长上升子序列

51. N皇后

 

174. 地下城游戏