传送门
分析
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x,y的范围-1e8~1e8，需要离散化。
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定义f[i][j]是左上角（ci,cj）右下角（c(i+1),c(j+1)）染色情况
代码实现
#include<bits/stdc++.h>
using namespace std;
#define MAXN 4010
int n, btop, ctop;
int a[MAXN][4];
int b[MAXN], c[MAXN];
int f[MAXN][MAXN];
map<int, int> Map;
int main()
{cin >> n;for (int i = 1; i <= n; i++){for (int j = 0; j < 4; j++){cin >> a[i][j];b[++btop] = a[i][j];}}sort(b + 1, b + btop + 1);b[0] = -1e9;for (int i = 1; i <= btop; i++)//离散化{if (b[i] != b[i - 1]){c[++ctop] = b[i];Map[b[i]] = ctop;}}for (int i = 1; i <= n; i++)for (int j = 0; j < 4; j++)a[i][j] = Map[a[i][j]];for (int k = 1; k <= n; k++)for (int i = a[k][0]; i < a[k][2]; i++)f[i][a[k][3]]++, f[i][a[k][1]]--;for (int i = 1; i < ctop; i++)for (int j = 1; j < ctop; j++)f[i][j] += f[i][j - 1];long long ans = 0;for (int i = 1; i < ctop; i++)for (int j = 1; j < ctop; j++)if (f[i][j])ans += (long long)(c[i + 1] - c[i]) * (c[j + 1] - c[j]);cout << ans << "\n";return 0;
}