Day2-260117|长度最小的子数组|区间和|螺旋矩阵II|开发商购买土地

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22class Solution {
    public int minSubArrayLen(int target, int[] nums) {
     int arr_length = nums.length;
     int result_length = Integer.MAX_VALUE;
     int sum = 0;
     int left = 0;

     for(int right = 0; right < arr_length; right++){
        sum += nums[right];
        //当右指针左边的数值大于目标值时候缩小窗口
        while(sum >= target){
            //进入while条件说明满足，先更新结果
            result_length = Math.min(result_length, right - left + 1);
            //缩小窗口
            sum -= nums[left];
            left++;
        }
     }   
     return result_length == Integer.MAX_VALUE ? 0 : result_length;
    }
}

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1 3

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9

sum[b] - (a == 0 ? 0 : sum[a - 1])

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33import java.util.Scanner; 

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
 
        int arr_length = sc.nextInt();
        int[] arr = new int[arr_length]; 
        int[] sum = new int[arr_length]; 
        
     
        int pre = 0;
        for (int i = 0; i < arr_length; i++) {
            arr[i] = sc.nextInt();
            if (i == 0) {
                sum[i] = arr[i];
            } else {
                sum[i] = sum[i - 1] + arr[i];
            }
        }
        
        while (sc.hasNext()) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            int result = sum[b] - (a > 0 ? sum[a - 1] : 0);
            System.out.println(result);
        }
        
        sc.close(); 
    }
}

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45class Solution {
    public int[][] generateMatrix(int n) {
        int result[][] = new int[n][n];
        int current = 1;

        int top = 0;
        int left = 0;
        int right = n - 1;
        int bottom = n - 1;
        
        while(left <= right && top <= bottom){
            //顶部
            for(int i = left; i < right; i++){
                result[top][i] = current;
                current++;
            }
            //右侧
            for(int i = top; i < bottom; i++){
                result[i][bottom] = current;
                current++;
            }
            //底部
            for(int i = right; i > left; i--){
                result[bottom][i] = current;
                current++;
            }

            //左侧
            for(int i = bottom; i > top; i--){
                result[i][left] = current;
                current++;
            }
            top++;
            left++;
            right--;
            bottom--;
        }
        if(n % 2 != 0){
            result[n/2][n/2] = current;
        }

        return result;
    }
}

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sum[i] - (total - sum[i])

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49import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int m = sc.nextInt();

        int[][] grid = new int[n][m];

        int[] rowSum = new int[n];
        int[] colSum = new int[m];

        int total = 0;

        // 读取数据 + 统计行和、列和、总和
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                grid[i][j] = sc.nextInt();
                rowSum[i] += grid[i][j];
                colSum[j] += grid[i][j];
                total += grid[i][j];
            }
        }

        int ans = Integer.MAX_VALUE;

        // 横向切割
        int prefix = 0;
        for (int i = 0; i < n - 1; i++) { // 不能切在最后一行
            prefix += rowSum[i];
            int diff = Math.abs(prefix - (total - prefix));
            ans = Math.min(ans, diff);
        }

        // 纵向切割
        prefix = 0;
        for (int j = 0; j < m - 1; j++) { // 不能切在最后一列
            prefix += colSum[j];
            int diff = Math.abs(prefix - (total - prefix));
            ans = Math.min(ans, diff);
        }

        System.out.println(ans);
    }
}